Drying apparatus

ABSTRACT

A drying apparatus comprising a cabinet for housing articles to be dried and an air conditioning plant including air cooling means to condense water from water vapor-laden air drawn in from the cabinet by a circulating fan and means to heat the air recycled back into the cabinet, the air cooling means and air heating means being the evaporator and condenser respectively of a refrigeration plant, a metered part of the circulating air only being passed over the evaporator by a second fan and part of the heat produced by the condenser being lost externally to the apparatus.

United States Patent 1 Clark 4] DRYING APPARATUS [76] Inventor: RonaldJohn Clark, 17 Bream Down Avenue, Weston-Super-Mare, England [22] Filed:May 25, 1971 [21] Appl. No.: 146,666

3 1943 Phipps 34/77 June 19, 1973 2,643,523 6/1953 Burgess 34/772,627,699 2/1953 Candor.... 34/76 3,270,530 9/1966 Czech 134/77 [57]ABSTRACT A drying apparatus comprising a cabinet for housing articles tobe dried and an air conditioning plant including air cooling means tocondense water from water vapor-laden air drawn in from the cabinet by acirculating fan and means to heat the air recycled back into thecabinet, the air cooling means and air heating means being theevaporator and condenser respectively of a refrigeration plant, ametered part of the circulating air only being passed over theevaporator by a second fan and part of the heat produced by thecondenser being lost externally to the apparatus.

7 Claims, 8 Drawing Figures PAIENIED JUN 1 9191s sum 2 or e USU 5N7 RNALD .J. Chm/e DRYING APPARATUS BACKGROUND OF THE INVENTION 1. Thisinvention relates to improvements in drying apparatus, particularly forthe removal of water from domestic articles such as clothing, andcomprises an air conditioning part arranged to work in conjunction withacabinet o'r closet, which may include racks for supporting wetarticles. The air conditioning part includes .an air cooling means andan air heating means formed by the evaporator and condenser respectivelyof a refrigeration machine, the evaporator serving to cool air passingthereover below its dew-point to condense out water, and the condenserserving to warm the air stream to produce effective drying conditions inthe recirculated air. The air is continually drawn in from the dryingcabinet and passed over the evaporator and condenser by a circulatingfan and then passed back into the cabinet.

In a drying apparatus of this type water is picked up from articles inthe cabinet by the warm dry circulating air and the water subsequentlycondensed and removed from the water vapor laden air stream by theevaporator. The water thus condensed is collected for disposal.

A particular advantage of drying apparatus of this type is the abilityto completely dry totally saturated articles in a reasonably shortperiod of time without using mechanical movement which has a damagingeffect on certain materials.

2. A drying apparatus is described in British Patent specification No.1133098 which has the characteristics above mentioned in addition to thefeature of dividing the return air-flow so that only a part thereofpasses through the evaporator, the remainder being bypassed. The purposeof this is an attempt to obtain optimum dehumidification conditions bypassing only a small volume of the total circulating air-flow over theair cooling means. It has been found, however, that in practice whilstthis arrangement does, to certain extent, increase efficiency a dryingapparatus constructed in accordance with this specification cannot bemade to work continuously. In other words the water extraction rateachieved at the commencement of the drying cycle will gradually declineduring operation until a set of conditions within the system is reachedwhich results in the water extraction falling to zero. The fact thatsuch an apparatus will not function to extract water on a continuousbasis, for as long as the machine is operated, is a seriousdisadvantage, particularly in the case of apparatus for domestic use.

It is a primary object of this invention to provide an improvement inthe above apparatus to enable a continuous drying cycle to be obtainedso that, irrespective of the length of time of running of the apparatus,said apparatus is always capable of extractingwater.

Another object is to provide a drying apparatus which is capable ofwater extraction over a widely varying range of external temperatures.

SUMMARY OF THE INVENTION within the apparatus and a bypass means wherebya part only of the air is passed over the evaporator. Alternatively, thecabinet of the drying apparatus can be constructed so as to yield partof the heat produced ex ternally to the apparatus itself.

According to another feature of the invention an auxiliary fan is usedto draw off a part only of the circulating air and pass same through theevaporator for cooling. By this means a steady and controlled amount ofair only is cooled at all times irrespective of the loading of thedrying chamber, which greatly changes the airflow cycled through theapparatus.

The drying apparatus may be constructed as a module containing theconditioning unit and having an air inlet and outlet arranged for usewith a separate cabinet which may form part of a dwelling, that is acupboard or closet.

A drying apparatus having both the features of dividing the condenser tolose heat externally, and provision of an auxiliary fan to provide anexact and metered airflow over the evaporator, has proved in practice tobe particularly advantageous and by correct design a closeddehumidification cycle can be obtained which is efficient and which willfunction over any length of time desired to continually extract waterfrom wet articles.

A further advantage is that, as it has now been found that provisionmust be made for heat loss from the sys tern, the cabinet containing theapparatus need not be insulated, the whole acting as a balancingheatexchanger.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fullyunderstood from the following description taken in conjunction with theaccompanying diagrammatic drawings, in which:

FIG. 1 shows a drying apparatus in which the condenser is arranged togive up part of its heat external to the apparatus.

FIG. 2 shows an apparatus of modified form in which the condenser givesup heat to water moving through the apparatus.

FIG. 3 shows an apparatus incorporating an auxiliary fan for passing ametered quantity of air over the evaporator.

FIG. 4 shows a side view of an air conditioning module incorporating acondenser arranged to give up part of its heat externally, and anauxiliary fan for passing a metered quantity of air over the evaporator.

FIG. 5 is a view looking in the direction X of FIG. 4.

FIG. 6 is a side view of a modified apparatus similar in operation toFIG. 4.

FIG. 7 is a plan view of the apparatus of FIG. 6 looking in thedirection Y, and

FIG. 8 is a comparative graph.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

FIG. 1 shows a drying apparatus generally of the type described inBritish Patent No. 1133098 and including a drying chamber 1, includingracks or rails 2 to hold articles, such as clothing, to be dried. Theair conditioning unit forming part of the apparatus has an air inlet 3and an air outlet 4, and a fan 5 arranged to circulate air from theinlet through the conditioning unit to the outlet.

The air stream at the inlet 2 is divided into two parts; roughly onethird passes upwards in the direction A and then down through an aircooling means 6 comprising a finned tube forming the evaporator of avapor compression refrigeration plant. The remaining two thirdsby-passes the evaporator and passes in the direction B to recombine withthe cooled air at C. The air passing through the evaporator is cooledbelow its dew-point and the water condensed therefrom is collected by adrip tray 7 and removed from the apparatus.

The recombined air stream C passes over the compressor 8 and receiver 9of the refrigeration plant and is directed upwardly by the fan and overthe coils 10 of the condenser forming part of the refrigerating plantand constituting an air heating means. The warm dry air emerges at theoutlet 4 and may be distributed by baffles 11 into the drying chamber 2.It has been found, however, that under practical conditions articleswithin the chamber 2 serve to adequately distribute the airflow withoutadditional means being provided.

According to the one aspect of this invention, in order to achieveoptimum dehumidification conditions for continuous operation, means areprovided to eject heat external to the apparatus, said means comprisingsplitting the condenser to form a second part 12 integral with the sidewall 13 of the apparatus. This second part of the condenser gives upheat to warm the cabinet and hence the air surrounding same.

The apparatus of FIG. 2 embodies a drying chamber 21 defined by aperforated wall member 21a, of which the perforations at the side 21bare of smaller size than those at the side 21c to ensure substantiallyeven air flow into the chamber 21. The air conditioning unit has aninlet 23 which again divides the air into two streams A and B. Thestream A passes over the evaporator 26 of a refrigerating plant andcondensed water is collected by drip tray 27.

The air stream recombines at C and is moved, by the circulating fan 25,over the compressor 28 of the refrig erating plant and then passed overcondenser 30 of the refrigeration plant to an inlet zone 24 of thedrying chamber.

The condenser of the refrigeration plant is divided into two parts, theone part 30 mentioned serving as the air heating means, the coils of theother part 32 being housed within the lower part of the apparatuscontaining water 31. An inlet 33 and outlet 34 for the water is providedwhich serves primarily as a medium for removing excess heat from therefrigerating cycle. A secondary feature is the use of the water forexternalpurposes such as in topping up heat requirements in feed waterused for washing machine installations.

The drying chamber 21 includes a rotatable drum 22 for housing articlesto be dried.

In the embodiments described the dividing of the condenser has beenfound to produce an efficient working cycle which may be operatedcontinuously. Under optimum conditions within the evaporator it has beenfound that in the heat pump cycle more heat is produced by the condenserthan is absorbed by the evaporator, and if all such heat is returned tothe circulating air stream then, during operation, the efficiency of thedehumidification cycle falls. By the division of the condenser to ejecta part of the heat external to the apparatus, either to ambient or somesuitable medium, the operating cycle can be stabilized at an optimumpoint. The external condenser should be sized in order to stabilize thesystem on the required condensing and evaporating conditions.

Ambient temperatures will also have an effect on the heat rejectedexternally and will affect the drying performance of the apparatus. Ahigh ambient temperature will increase the system temperatures andpressures, and although drying performance may remain satisfactory,mechanical limitations may be exceeded. A low ambient temperature willdecrease system temperatures which will decrease system temperatures,which will reduce the drying performance. The external condenser musttherefore be designed taking into account the ambient temperatureconditions in which the apparatus will be used.

Because heat loss is designed into the apparatus according to theinvention it is unnecessary to thermally insulate the cabinet of theapparatus, and in such a case the whole cabinet may form a means forejecting heat to the environment to produce the stabilized conditions.

When the apparatus is started there is a certain delay before waterextraction commences, due to the time required before operatingconditions are established. To overcome this a heater may be included toboost the drying performance during the initial warming up period. Theheater may also serve to improve the operation when the apparatus usused in ambient conditions which are lower in temperature than that forwhich the apparatus is designed.

The drying apparatus shown in FIG. 3 incorporates an auxiliary fan inaccordance with the second aspect of this invention.

As shown, a drying chamber 40 adapted to contain articles to be dried iscontained within a cabinet also housing an air conditioning unit. Thesaid unit has 'an air inlet shown generally as 41 and an air outlet 42,and includes a fan 43 for circulating air from the inlet to the outlet.Air at the inlet 41 is divided to produce a stream A which passesupwards and is drawn through an auxiliary fan 44 and then directeddownwards to flow through an air cooling means 45, formed by theevaporator of a refrigeration plant 52. Water condensed out of the airby the evaporator is collected at 46. The air stream A then combineswith a stream B, which bypasses the evaporator, in the zone C. The fan43 directs the air stream over an optional electric heater 47 andupwards over the coils 48 of the condenser of the refrigeration plant,and into the drying chamber via the outlet 42. The conditioned airpasses into the chamber 40 via a perforated ceiling 49 to be drawndownwards to the inlet 41, through the articles to be dried.

A desiccant bed 50 may be provided.

Air already existant in the chamber 40 is drawn through inlet stream Bthrough the desiccant bed 50, continuing in an upward direction over thecondenser coil 48 into chamber 40. Because of the designed suctionpressure in the chamber percent of the air is continually recirculateddirect from chamber 40 through the condenser 48. However, due to densitydifferential, 10 percent of the moist air travels in direction A via thefan orifice and in a downward direction across the evaporator 45 andinto the zone C. Air passing through the clothes in chamber 40 picks upmoisture, some of which is immediately absorbed by the desiccant bed 50.The air is then further warmed by the condenser 48, completing thecycle.

The small percentage of air passing over the evaporator 45 gives up itsmoisture due to condensation on the evaporator coil. This processcontinues until such time when a sensing device in the chamber, set at apredetermined humidity, activates the fan 44 which immediately changesthe percentage ratio from 90 percent to approximately 70 30 percent. Thecycling of this fan in sequence with the humidity-stat creates the bestsituation for dehumidification which is a variable characteristic,therefore creating a maximum effect drying cycle.

When the clothes are dry an air exhaust 51 is opened and the door on theapparatus is also left open. A programmed regenerating cycle then occurswhich is timed to drive off the moisture held in the desiccant bed.

In contrast to passively splitting the air-flow, the auxiliary fanallows a precise and metered quantity of air to be passed to theevaporator, regardless of the load conditions on the main fan 43 createdby resistance to air-flow through the chamber 40.

Once condenser and evaporator conditions have been fixed there exists aunique air-flow that will utilize the total evaporator capacity, therebygiving the optimum dehumidification. A variation from this air flow willdecrease the moisture extraction since a reduction will not use thetotal evaporator capacity, whereas an increased air-flow will produce anincrease in the ratio of sensible to latent heat required to bring theair to or below the dew point.

It has been found that varying loadings in the chamber 40 affect the airflow rate, but by provision of the auxiliary fan the metered air flowover the evaporator results in optimum dehumidification for allloadings.

The drying apparatus shown in FIGS. 4 and 5 cmbodies both the featuresof the divided condenser and the auxiliary fan to produce an apparatusof particular utility for domestic purposes. The apparatus broadlycomprises an air conditioning modular part 60 used in conjunction with adrying chamber 61 for housing articles to be dried. The chamber 61 canbe formed by a cupboard or closet of an existing dwelling or may form,together with the unit 60, an integral apparatus.

The conditioning unit embodies a centrifugal drum fan 62 which draws airin from the chamber 61 through an inlet 63, and passes the air out backinto the chamber through an outlet 64. The lower part of the unit housesthe compressor 65 of a vapor compression refrigeration system, thecondenser of which system is divided into two parts, the one 66 beingpositioned near the outlet 64 and serving as the air heating means, theother part 67 being located in a recess 68 on the side of the unit. Therecess forms a cavity through which air may flow by convection over thepart of the condenser 67, the assembly forming a means by which surplusheat may be ejected externally to the apparatus.

The air cooling means comprises an evaporator 69 and an auxiliary fan 70contained within a housing in the unit. The fan 70 serves to draw off atB a metered amount of air from the circulating stream A and pass sameover the evaporator where water vapor is condensed and extracted atanoutlet 71. The air passes back into the main stream A at C, and thecombined streams are passed over the condenser 66, serving as theheating means, and back into the chamber 61.

This apparatus embodying both features of the invention provesparticularly advantageous when used in a domestic drying system, andFIG. 8 illustrates at (a) typical water extraction against time for theapparatus of FIGS. 4 and 5, whereas at (b) the extraction is shown for asystem without the divided condenser and auxiliary fan. As shown bycurve (b), due to conditions within the refrigeration cycle beingunstabilized, the compressor will cut out after a period of operation,due to stalling, and will remain cut-off until conditions return tonormal. The actual cut-off point will depend on the protector used inthe compressor, but will result in a discontinuous operation asillustrated. The curve of (c) shows the typical performance of anapparatus without provision of a metered quantity of air across theevaporator, i.e. no auxiliary fan. In this case the operation iscontinuous but water extraction rates are much lower, representing lessefficient operation.

FIGS. 6 and 7 show an apparatus similar to that of FIGS. 4 and 5 and thesame references are used to indicate parts of like function. The airinlet to the conditioning unit comprises two streams A and A. The streamA passes direct to the inlet of the main fan 62, whilst the stream A isdrawn in over the evaporator 69 by a smaller auxiliary fan and passed tothe inlet of the main fan constituting the mixing zone C for the two airstreams. The air continues through a space containing the compressor 65and is warmed by passage over the condenser 66 and passed to the outlet64.

The auxiliary fan 70 again provides for the passage of a precise andmetered quantity of air over the evaporator 69 and performs anadditional function of cooling the bearings of the main fan 62. Thecondenser is divided into two parts, the one 66 serving as the airheating means and the other 67 forming a convector heater located on theouter wall of the apparatus for dissipating heat externally of theapparatus.

In the embodiments of FIGS. 4 to 7 the loss of heat from the condenserpart 67 may be by natural convection or assisted by forced draught.

The rate of dehumidification that can be obtained from such a system isdependent. on a number of parameters, including type and characteristicsof the compressor, type of refrigerant, condensing and evaporatingtemperatures, air flow rate and temperature and humidity, and as heat islost externally to the cycle, the ambient temperature. The flow rate,temperature and humidity of the air affect the mass transfer rate ofmoisture from the surface of items being dried and are directlyconnected with the drying rate that can be achieved.

At given evaporator temperature lowering the condenser temperature willincrease the evaporator capacity implying a greater moisture extractionrate. This, however, produces a lowering of air temperature which isdetrimental to mass transfer rates. There thus exists an ideal condensercondition for a given evaporator condition at which moisture extractedby the evaporator equals the mass transfer rate of moisture from the wetitems in the airstream.

From compressor characteristics, refrigerant flow and hence evaporatorduty both increase with evaporator temperature implying a greatermoisture extraction rate. However, a higherair flow over the evaporatoris required to utilize its total capacity. As air of percent relativehumidity cannot be achieved this results in an increasing ratio ofsensible to latent heat for moisture extraction. Thus for a givencondenser condition there exists an optimum evaporator condition.

The invention enables these requirements to be realized in practice andprovides a drying apparatus with a stabilized cycle and efficientoperation.

I claim:

1. An improvement in a drying apparatus including a chamber to containarticles to be dried and an air conditioning unit having air displacingmeans for drawing air. in from said chamber and passing same over theevaporator of a refrigerating plant, and then over the condenser of saidrefrigerating plant, and back into said chamber, wherein the improvementcomprises in combination provision of means whereby part of the heatproduced by said condenser is ejected externally of said apparatus and abypass means whereby a part only of the air is passed over theevaporator.

2. A drying apparatus as claimed in 1, wherein the condenser is in twoparts one part giving up heat to a flowable medium for use external tothe apparatus.

3. A drying apparatus as claimed in claim 2, wherein the by-pass meansis provided at the inlet to the air conditioning unit whereby only apart of the circulating air ing air in from said chamber and passing apart only of same over an evaporator of a refrigerating plant, the airstream then passing over the condenser of the refrigerating plant andback into said chamber, wherein the improvement comprises provision of asecond auxiliary air displacing means serving to pass a metered quantityof air, constituting a part only of the air drawn in, over saidevaporator, the condenser being divided into two or more parts, one ofsaid parts serving to heat the air, the other part giving up heatexternally to said apparatus.

5. A drying apparatus as claimed in claim 4, wherein the other part ofthe condenser is locatedin a side wall of the apparatus and forms aconvector heater assisted, if necessary, by forced draft producingmeans.

6. A drying apparatus as claimed in claim 5, wherein the evaporator andauxiliary air displacing means comprise an assembly positioned withinthe air conditioning unit and located in the recirculating air stream.

7. A drying apparatus as claimed in claim 5, wherein the inlet to theair conditioning unit is divided into two parts, one part directing airover the evaporator, and incorporating the auxiliary air displacingmeans.

* III 4K

1. An improvement in a drying apparatus including a chamber to containarticles to be dried and an air conditioning unit having air displacingmeans for drawing air in from said chamber and passing same over theevaporator of a refrigerating plant, and then over the condenser of saidrefrigerating plant, and back into said chamber, wherein the improvementcomprises in combination provision of means whereby part of the heatproduced by said condenser is ejected externally of said apparatus and abypass means whereby a part only of the air is passed over theevaporator.
 2. A drying apparatus as claimed in 1, wherein the condenseris in two parts one part giving up heat to a flowable medium for useexternal to the apparatus.
 3. A drying apparatus as claimed in claim 2,wherein the by-pass means is provided at the inlet to the airconditioning unit whereby only a part of the circulating air passesacross the evaporator.
 4. An improvement in a drying apparatus includinga chamber to contain articles to be dried and an air conditioning unithaving air displacing means for drawing air in from said chamber andpassing a part only of same over an evaporator of a refrigerating plant,the air stream then passing over the condenser of the refrigeratingplant and back into said chamber, wherein the improvement comprisesprovision of a second auxiliary air displacing means serving to pass ametered quantity of air, constituting a part only of the air drawn in,over said evaporator, the condenser being divided into two or moreparts, one of said parts serving to heat the air, the other part givingup heat externally to said apparatus.
 5. A drying apparatus as claimedin claim 4, wherein the other part of the condenser is located in a sidewall of the apparatus and forms a convector heater assisted, ifnecessary, by forced draft producing means.
 6. A drying apparatus asclaimed in claim 5, wherein the evaporator and auxiliary air displacingmeans comprise an assembly positioned within the air conditioning unitand located in the recirculating air stream.
 7. A drying apparatus asclaimed in claim 5, wherein the inlet to the air conditioning unit isdivided into two parts, one part directing air over the evaporator, andincorporating the auxiliary air displacing means.